Focusing particles

The orientation parameters obtained from the far-from-focus particle images in the focal pair are used as the starting point for processing the close-to-focus particles. Because of the poor S/N ratio of low-resolution features, the center and orientation parameters of the close-to-focus particles cannot be reliably determined by directly using the orientation... 

For ensuring that only in-focus particles are considered for size measurement, the upper and lower threshold levels have to be set appropriately Extensive studies on the required threshold level have been performed by Hardalupas et al. (1994). With appropriate settings the sizing error can be reduced to about 10%. The shadow-Doppler technique is presently being developed further. Recently, first attempts to measure the particle mass flux were also made (Maeda et al. 1996 a)). 

Nanoactive MgO Plus particles when suspended at 50 to 250 ppm in HESS or DMEM and gently stirred formed a 10 to 50 cm halo that macroscopically resembled a tenuous and porous lattice. The lattices persisted for 2 to 4 day solubility smdies conducted at 22°C or 37°C. We interpreted this process as the formation of aggregates marginally smaller than the size needed to settle out of solution with gentle stirring. The porous lattices focused particles that deposited in deep lung and moved to the ELF near their point of dissolution (25, 26). 

An alternative method is electrokinetic focusing, which uses a direct current electric field (at high voltages of 1 kV) to focus particles and Uquids into a narrow stream. Typically, the sample fluid stream is driven along the central channel of a cross-shaped channel. As the sample enters the intersection, three fluid streams meet and the sample stream is focused into narrow stream. Dielectrophoresis (DEP) can also be used for sample focusing. DEP is the movement of polarized particles in a nonuniform electric field. This phenomenon is explained further in the next section. The main advantage of this... 

Figure 6 demonstrates a continuous electroki-netic sorting of polyst3rene particles by size and surface charge simultaneously in an asymmetric double-spiral microchaimel [3]. The mixture of nonfluorescent 5 pm, nonfluorescent 10 pm, and fluorescent 10 pm particles is resuspended in 0.1 mM phosphate buffer. As the buffer solution is more conductive, all three t3q>es of particles undergo negative C-iDEP in the spiral. Under the application of a 33 kV/m DC electric field, the initially scattered particles in Fig. 6b are focused by C-iDEP to a tight stream flowing near the outer sidewall of the 100 pm wide first spiral as seen from Fig. 6c. Subsequently in the second spiral whose width increases from 100 pm to 200 pm, the focused particles are all displaced from the inner to the outer wall by C-iDEP at a particle size- and charge-dependent rate or, more accurately, the particle dielectrophoretic to electrokinetic mobility ratio in Eq. 6.

The consequence is the split of the single particle stream into three sub-streams at the exit of the second spiral as illustrated in Fig. 6d. It is important to note that the two spirals must be of dissimilar dimensions (here, width is varied) to break the symmetry. Otherwise, the focused particles in the first spiral are simply displaced from the inner to the outer sidewall in the secraid spiral without being separated. 

Singh DK, Panigrahi PK (2010) Improved digital holographic reconstmction algorithm for depth error reduction and elimination of out-of-focus particles. Opt Express 18(3) 2426... 

The depth of the field for a volume-illuminated p-PIV setup does not define precisely the thickness of the measurement plane because only the sharply focused particles contribute to the correlation function. The depth of the field is defined as twice the distance from the object plane to the plane in which the object is regarded as unfocused. The depth of correlation depends on the axial distance from the object plane in which a particle becomes sufficiently out of focus so that it no longer contributes significantly to the peak in the particle-image correlation function and can be calculated according to... 

There are additional considerations for CPAA. The requirement for an accelerator essentially limits the use to some substantial facilities the primary applications of which are in other research fields, and CPAA must obtain a share of the beam time. Generally, only one beam is available, i.e., only one sample or one comparator standard is irradiated at a time. These disadvantages maybe outweighed by combining the quantitative information with spatial and depth information, which can be obtained using focused particle beams and modulation of particle energy to change reaction depth. CPAA has been discussed in more detail by Strijckmans (1994). 

Techniques that can improve statistical sampling are often crucial in these approaches. An excluded-volume map can improve efficiency by focusing particle insertions into free volume voids [159,177-179]. Specially designed Monte Carlo moves allow polymer chain fluctuations within... 

---